formula feeding

Ayesha
Hello everyone one need an advice is it ok to give a formula milk to a new born baby is almost 3.5 weeks old I'm giving my lo this because he always gets hungry while breastfeeding I do breastfed him with In a gap of 2 hours but he remains hungry will this help and I'm giving him similac total comfort milk which formula milk are you using 
And how many ounces ??